I had email contact with CS-Lab
And they say this:
It is about that although the C axis doesn't have the home switch the home diode of C axis must light green so the fault you have showed in a picture won't show up.
It is enough to press "Ref C" w 'Diagnostic Alt-7" or improve VB macro of "Ref All Home" (this button does the homing for x, y, z axes and there is no homing for b and c).
They also attached a video, I will try to upload it to youtube later.
It is very clear what is happening, I try this later on the machine and post the feedback.